The present invention relates to a lens barrel for use in a video camera or the like.
Recently there is a demand for small-sized lens barrels for video cameras whose body-size is being reduced. Faster zooming or focusing is also required.
Hereinafter, a conventional lens barrel will be described.
In general, a lens barrel for a video camera includes four lens groups. Movable lens groups of the four lens groups are moved in a direction of an optical axis by guiding along a guide pole for the purposes of zooming and focusing. The lens barrel includes a fixed lens group, a lens group movable on the optical axis for zooming, another fixed lens group, a lens group movable on the optical axis for focusing, an iris unit, and an imaging plane. The zooming lens group and the focusing lens group are held by a zooming lens frame and a focusing lens frame, respectively. A zooming actuator and a focusing actuator for driving the zooming lens moving frame and the focusing lens frame in the optical axis direction, respectively, each include a stepping motor. The zooming and focusing stepping motors each include a screw on the respective output axes. The zooming lens moving frame and the focusing lens frame are linked to each other by a linkage. Two guide poles are used to hold the zooming lens moving frame and the focusing lens frame so that the frames can freely move in the optical axis direction. In such a lens barrel, when a current is supplied to the zooming stepping motor via an electrical signal line, the output axis is rotated so that the linkage which is engaged with the screw of the zooming stepping motor is moved in the optical axis direction. The zooming lens moving frame, i. e., the zooming lens group, which is engaged with the linkage, is then moved in the optical axis direction. Similarly, when a current is supplied to the focusing stepping motor via the electrical signal line, the output axis is rotated so that the linkage which is engaged with the screw of the focusing stepping motor is moved in the optical axis direction. The focusing lens frame, i.e., the focusing lens group, which is engaged with the linkage, is then moved in the optical axis direction.
Such a conventional structure has the following problems.
(1) The stepping motor used as the actuator in the conventional lens barrel can be stopped at a predetermined position by rotating the motor by an angle corresponding to a predetermined number of pulses. However, since the driving control of the stepping motor is an open loop, there are the following problems: the precision in the stopping positions is poor; a hysteresis property exists; the number of revolutions is relatively low, and the like. Therefore, when the stepping motor is used as a driving power source of a transporting mechanism for the zooming or focusing lens moving frame, the zooming or focusing speed is slow. Japanese Laid-Open Publication No. 8-266093 proposes a stepping motor system having an encoder as a solution to this above problem. As is disclosed by the publication, a sensor is provided which detects the rotational angle of a stepping motor. The sensor results in the control system being a closed loop, thereby making it possible to achieve high-speed driving. Japanese Laid-Open Publication No. 10-225083 proposes a linear actuator system which can track the changing positions of the focusing group using a voice type linear actuator. Such a linear actuator system has a high-speed response capability and lower power consumption.
Therefore, the lens driving system may be optimized by adopting a stepping motor having an encoder for driving the zooming lens group; and by adopting a linear actuator for moving the focusing lens group, for the purpose of the high-speed response capability and low power consumption. Such a system generally includes a magnetoresistance sensor (hereinafter referred to as a magnetic sensor) as a position detection sensor in order to increase the precision of the position detection.
A small-sized and lightweight lens barrel is required for recent small-sized and lightweight video cameras. Therefore, intervals of components included in the lens barrel tend to be decreased. When a conventional magnetic sensor is affected by an external disturbance magnetic field, the output of the sensor is distorted, causing a problem in that the performance of the actuator is deteriorated. Magnetic flux leakage from a driving magnet occurs in the above-described stepping motor having an encoder and linear actuator. Such magnetic flux leakage is not negligible in the case of a small-sized lens barrel since the gaps between the parts thereof are narrow. In particular, the driving magnet of the linear actuator has an adverse influence on the magnetic sensor of the stepping motor having an encoder. Conventionally, an additional part such as a magnetic shield has been used to address the magnetic flux leakage problem. However, such a magnetic shield leads to an increase in cost. The provision of a space for the magnetic shield hinders achievement of the small-sized lens barrel. Therefore, a system including the small-sized and lightweight lens barrel, the stepping motor having an encoder, and the linear actuator cannot realize the high-speed response capability and low power consumption in driving the zooming and focusing lenses.
(2) A small-size, lightweight and high-magnification lens barrel poses a problem that hand-shake makes it difficult to obtain a stable image at the furthermost focusing point. A conventional solution to the problem is an electric hand-shake compensation system. The compensation extent needs to be expanded with an increase in the degree of hand-shake in the smaller-sized, lighter-weight, and higher magnification lens barrel. The compensation extent to the hand-shake in the electrical compensation system depends on the number of pixels in the CCD, requiring many pixels. Smaller-sized CCDs and higher picture quality video cameras pose limitations to the increased number of pixels allowed in the CCD, whereby the electric hand-shake compensation system does not work effectively.
Optical hand-shake compensation systems have been proposed whose compensation extents are large and in which high picture quality is obtained. As one of the optical hand-shake compensation systems, Japanese Laid-Open Publication No. 3-186823 discloses a so-called inner-shift system in which the hand-shake is compensated by moving a predetermined lens group (shift lens group) in a direction perpendicular to the optical axis. In the inner shift system, a lens group required for focusing is also used as the shift lens group for compensating the hand-shake. Therefore, a short, small-sized, and lightweight lens barrel can be realized.
However, two additional actuators are required for moving the compensation lens group in a direction perpendicular to the optical axis. In addition to the actuators for zooming, focusing, and the iris included in the conventional lens barrel, two shift actuators are required for compensating the hand-shake. That is, five actuators need to be provided in a single lens barrel. This increased number of actuators makes it difficult to obtain a small-sized lens barrel, which runs against the recent tide of small-sized lens barrels. In this case, it is important to arrange these actuators in a compact manner.
(3) As indicated in problem (1), when the stepping motor having an encoder using the magnetic sensor, and the linear actuator are used as the zooming and focusing actuators, respectively, magnetic flux leakage from the two shift actuators for image shake compensation occurs, adversely affecting the magnetic sensor.
Therefore, an object of the present invention is to provide a lens barrel which can eliminate the adverse effect of the magnetic flux leakage occurring in the actuator on the magnetic sensor.
A lens barrel according to the present invention includes a first lens group; a second lens group; a third lens group; a first actuator for driving the first lens group; a second actuator for driving the second lens group; and third and fourth actuators for driving the third lens group. At least one of the first through fourth actuators is provided at a position such that magnetic flux leakage from at least one of the first through fourth actuators is canceled. Thereby, the above object is achieved.
The first actuator may include a stepping motor; a first magnet in the shape of a barrel or column, magnetized to have multiple poles in a circular direction, and attached coaxially to the stepping motor in such a manner as to rotate; and a first magnetic sensor provided opposing an outer edge of the first magnet. The second actuator includes a second magnet magnetized perpendicular to a driving direction; a yoke; a coil provided at a predetermined gap from the second magnet, capable of freely moving in the driving direction when a current is supplied thereto in such a manner as to flow in a direction perpendicular to magnetic flux generated by the second magnet; and a second magnetic sensor. The first magnetic sensor may be provided at a position such that magnetic flux leakage from a magnetic circuit including the second magnet and the yoke is canceled.
The second actuator may include a magnet magnetized perpendicular to a driving direction; a yoke; a coil provided at a predetermined gap from the magnet, capable of freely moving in the driving direction when a current is supplied thereto in such a manner as to flow in a direction perpendicular to flux generated by the magnet; and a magnetic sensor. The magnetic sensor may be provided at a position such that magnetic flux leakage from at least one of the third and fourth acturator is canceled.
The third actuator may include a third magnet, the fourth actuator includes a fourth magnet; and the third magnet and the fourth magnet are provided in such a manner that the magnetization of the third and fourth magnets is reversed when viewed in the center of an optical axis.
The first actuator may include a stepping motor; a first magnet in the shape of a barrel or column, magnetized to have multiple poles in a circular direction, and attached coaxially to the stepping motor in such a manner as to rotate; and a magnetic sensor provided opposing an outer edge of the first magnet. The third and fourth magnets may be provided at positions such that magnetic flux leakage to the magnetic sensor is canceled.
The lens barrel may further include first and second lens moving frames holding the third lens group and capable of being smoothly moved in first and second directions perpendicular to an optical axis, respectively. One of the third or fourth actuators provided at an optical axis imaging plane side may be provided overlapping the lens moving frame provided at an optical axis object side when viewed in the optical axis direction.
The second actuator may be provided at an optical axis imaging plane side of one of the third and fourth actuators provided at an optical axis object side, overlapping one of the third and fourth actuators, when viewed in the optical axis direction.
The lens barrel may further include first and second lens moving frames holding the third lens group and capable of being smoothly moved in first and second directions perpendicular to the optical axis, respectively; and a fixing frame holding the first and second lens moving frames, leaving the first and second lens moving frames capable of being smoothly moved. The fixing frame may include a depression in a portion surrounded by the third and fourth actuators; and the first actuator is provided in the depression.
The lens barrel may further include an actuator for driving an iris. The actuator for driving the iris may be provided at the optical axis object side of one of the third and fourth actuators provided at an optical axis imaging plane side.
The lens barrel may further include first and second lens moving frames holding the third lens group, provided at different heights with respect to an optical axis, and capable of being smoothly moved in first and second directions perpendicular to the optical axis; a first light emitting portion incorporated into the first lens moving frame for detecting a position of the first lens moving frame; and a second light emitting portion incorporated into the second lens moving frame for detecting a position of the second lens moving frame. The first and second light emitting portions may be provided at substantially the same height when viewed in the optical axis direction.
The lens barrel may further include first and second lens moving frames holding the third lens group, and capable of being smoothly moved in first and second directions perpendicular to an optical axis; and a fixing frame fixing the first and second lens moving frames, leaving the first and second lens moving frames capable of being smoothly moved. The third actuator may drive the first lens moving frame. The fourth actuator may drive the second lens moving frame. The lens barrel may further include a first flexible print cable electrically connected to the third actuator; and a second flexible print cable electrically connected to the fourth actuator. One end of the first flexible print cable may be fixed to the first lens moving frame at a side thereof opposite to the third actuator with respect to the optical axis and at the same side as that of the fourth actuator. One end of the second flexible print cable may be fixed to the second lens moving frame at a side thereof opposite to the third and fourth actuators with respect to the optical axis. Other ends of the first and second flexible print cables may be fixed to the fixing frame at a side thereof opposite to the fourth actuator with respect to the optical axis, being substantially parallel to a direction along which the first lens moving frame is smoothly moved.
The first flexible print cable may be provided at an outside from the center of the optical axis with respect to the second flexible print cable.
The first and second flexible print cables may be provided at different heights with respect to the optical axis of the third lens group.
Moving portions of the first and second flexible print cables and an outline of the fixing frame corresponding to the moving portions of the first and second flexible print cables may be substantially in the shape of a circular arc. The moving portions of the first and second flexible print cables may move along the fixing frame.
Another lens barrel according to the present invention includes a first lens group; a second lens group; a third lens group; a first actuator for driving the first lens group; a second actuator for driving the second lens group; third and fourth actuators for driving the third lens group; first and second lens moving frames holding the third lens group and capable of being smoothly moved in first and second directions perpendicular to an optical axis; and a fixing frame fixing the first and second lens moving frames, leaving the first and second lens moving frames capable of being smoothly moved. The third actuator drives the first lens moving frame. The fourth actuator drives the second lens moving frame. The lens barrel further includes: a first flexible print cable electrically connected to the third actuator. A second flexible print cable electrically connected to the fourth actuator. One end of the first flexible print cable is fixed to the first lens moving frame at a side thereof opposite to the third actuator with respect to the optical axis and at the same side as that of the fourth actuator. One end of the second flexible print cable is fixed to the second lens moving frame at a side thereof opposite to the third and fourth actuators with respect to the optical axis. Other ends of the first and second flexible print cables are fixed to the fixing frame at a side thereof opposite to the fourth actuator with respect to the optical axis, being substantially parallel to a direction along which the first lens moving frame is smoothly moved. Thereby, the above-described object is achieved.
The first flexible print cable may be provided at an outside from the center of the optical axis with respect to the second flexible print cable.
The first and second flexible print cables may be provided at different heights with respect to the optical axis of the third lens group.
Moving portions of the first and second flexible print cables and an outline of the fixing frame corresponding to the moving portions of the first and second flexible print cables may be substantially in the shape of a circular arc. The moving portions of the first and second flexible print cables may move along the fixing frame.